1. Field of the Invention
The present invention relates to an apparatus and method for successively inspecting a plurality of patterns provided on a surface of a sample such as a wafer or a mask by use of an electron beam and, more particularly, to a configuration for detecting at least one of secondary electrons, reflected electrons, and back-scattered electrons from the surface of the sample irradiated by the electron beam.
2. Related Background Art
With recent increase in integration of LSI, the detection sensitivity required for detection of defect on the surface of the sample such as the wafer or the mask is becoming higher and higher. For example, where 256M-DRAM is formed on the wafer of the line width 0.25 .mu.m, the detection sensitivity necessary for this wafer is that enough to detect a defect in the dimension of 0.1 .mu.m. Desires are also increasing for inspection apparatus satisfying the demand for increase in the inspection speed, as well as the increase in the sensitivity for detection of defect. In order to meet these demands, surface inspection devices (pattern inspection apparatus) utilizing the electron beam have been developed.
An example of the conventional pattern inspection apparatus using the electron beam is the inspection apparatus, for example, described in Japanese Laid-open Patent Applications No. Hei 5-258703 (U.S. Pat. No. 5,502,306) and No. Hei 7-249393 (U.S. Pat. No. 5,576,833).
FIG. 1 is a drawing to show the configuration of the conventional pattern inspection apparatus disclosed in above Japanese Laid-open Patent Application No. Hei 7-249393. This conventional pattern inspection apparatus is composed of a primary column 81, the primary column 81 consisting of an electron gun having a rectangular cathode for generating a rectangular electron beam and a quadrupole lens system, and a projection type secondary electron detecting column (secondary column) 84 for detecting secondary electrons or reflected electrons from the sample surface (electron beam irradiation area 85) being an inspected object. When the primary column 81 emits the electron beam (primary beam) to the electron beam irradiation area 85 on the sample 82, the secondary beam 83 of secondary electrons or the like from the electron beam irradiation area 85 is guided to an electron incident surface of electron detector 86 by an electron lens system for beam shaping provided in the secondary column 84. Then an electron image of the electron beam irradiation area 85 is taken as electric signals into detection signal processing circuit 87. By this arrangement wherein the electron optical system is composed of the rectangular cathode and quadrupole lens system, the electron beam irradiation area 85 on the sample 82 irradiated by the primary beam can be shaped readily and arbitrarily. This conventional pattern inspection apparatus is characterized in that high detection sensitivity is achieved and the inspection time for scanning the entire surface of sample can be decreased largely, by generation of the rectangular electron beam with an appropriate aspect ratio.
Next, various detecting systems have been proposed as secondary electron detecting systems for detecting the secondary electrons from the electron beam irradiation area in the surface of sample. An example is a secondary electron detector comprised of MCP/fluorescent screen/linear image sensor. FIG. 2 is a cross-sectional view to show the structure of the conventional secondary electron detector. The secondary electrons emitted from the electron beam irradiation area in the surface of sample travel through the secondary electron detecting column and then are multiplied by microchannel plate (MCP) 71. A fiber optic plate (FOP) the input surface of which is coated with a fluorescent film 72 is located behind this MCP 71. A group of electrons multiplied by the MCP 71 are converted to light by the fluorescent film 72 and thereafter the electrons are guided through the FOP 73 into MOS linear image sensor 74 to be further converted to electric signals.